CN1191108C

CN1191108C - Method for removal of water from gases using superheated zeolites

Info

Publication number: CN1191108C
Application number: CNB998138495A
Authority: CN
Inventors: D·弗伦克尔; H·H·芬克; G·科珀
Original assignee: Matheson Tri-Gas Inc
Current assignee: Matheson Tri-Gas Inc
Priority date: 1998-10-06
Filing date: 1999-10-06
Publication date: 2005-03-02
Anticipated expiration: 2019-10-06
Also published as: KR20010075591A; HK1042662B; WO2000020101A9; US6110258A; JP2002526237A; CA2345968A1; KR100454429B1; HK1042662A1; WO2000020101A1; EP1163041A4; EP1163041A1; CN1328480A

Abstract

A method for removing trace moisture from a gas is disclosed. The method involves heating a zeolite having a high silica-to-alumina ratio to about 400 DEG C to remove physically absorbed water from the zeolite, followed by heating the zeolite to a temperature in excess of 650 DEG C, to form a superheated zeolite. Heating to temperatures of 650 DEG C or above is believed to cause dehydroxylation of the zeolite. A method for the preparation of a dehydroxylated zeolite is also disclosed. The superheated zeolite is contacted with the gas, thereby adsorbing water from the gas. A dehydroxylated zeolite for removing trace moisture from a gas wherein the zeolite has a high silica-to-alumina ratio and a low level of metallic impurities is also disclosed. The zeolite and methods of the invention are particularly useful for removing trace water from acid gases such as hydrogen chloride and hydrogen bromide.

Description

Method for removing water from gas using superheated zeolite

Technical Field

The present invention relates to a method for removing moisture from gases, particularly acid gases, using a high silicon-to-aluminum ratio zeolite purifier that has been heated to about 650 ℃. The invention also relates to a process for preparing dehydroxylated zeolites.

Background

A variety of hydride, halide and bulk gases are used in the production of semiconductor devices and materials. As semiconductor geometries become smaller and smaller, devices become more complex, and the purity of these gases becomes more and more important for the promise and success of semiconductor production.

Water contamination in acid gases used in semiconductor manufacturing is particularly disadvantageous for a number of reasons. Even trace amounts of moisture in acid gases such as hydrogen chloride (HCl) and hydrogen bromide (HBr) can cause corrosion of the piping, valves and flow meters used to process these gases in semiconductor manufacturing. The presence of moisture in these gases can also cause corrosion of the walls of the cylinders in which they are stored. This corrosion results in the generation of metal particle contaminants that can become incorporated during the manufacture of the semiconductor device. In addition, certain processes used in semiconductor manufacturing can decompose moisture present in the process gas into H₂And O₂. The presence of these gases can lead to the formation of gaseous contaminants, particularly oxides, which can also be incorporated into semiconductor devices. Semiconductor devices contaminated with metal particles and oxide impurities severely degrade device performance and often result inThe device is defective or even incapable of performing its function. In addition, corrosion due to the presence of water in these gases results in the need for frequent replacement of expensive piping, manifolds, valves and other gas handling equipment.

Many materials have been developed for removing moisture from acid gases. One of these is chlorosilylated alumina which is effective in removing trace amounts of moisture from hydrogen chloride, hydrogen bromide, chlorosilanes, and chlorine. Such materials include octahedral alumina substrates with Al-O-Al bonds functionalized with chlorosilyl groups. This material removes moisture from a gas by irreversible chemical reaction of chlorosilyl groups on its surface with water, which can remove moisture to a level of 0.1ppm or less.

The use of chlorosilylated alumina to remove moisture from acid gases has a number of disadvantages. The preparation of such materials is complex and expensive, involving the use of silicon tetrachloride (SiCl), which is itself a corrosive material₄) And (4) processing. Furthermore, chlorosilylated alumina is only suitable for use with low pressure HCl, i.e., HCl at about 50 psig or less. Under high pressure, HCl reacts with alumina to produce aluminum trichloride (AlCl) which contaminates the purified gas stream₃Or dimer Al₂Cl₆). In the case of HBr, contamination of the aluminum halide occurs even at low pressures, since HBr is more reactive than HCl and AlBr₃(Al₂Br₆) Specific AlCl₃Is about an order of magnitude higher. The exudation of aluminum from chlorosilylated alumina purifiers in this manner causes degradation of the chlorosilylated alumina structure, resulting in particulate contamination of the gas and requiring frequent replacement of such solid purifiers. In addition, this material requires a preconditioning step with a halide acid gas, which begins to produce water, with an accompanying increase in temperature to 120-. This preconditioning step is time consuming and requires the use of large amounts of expensive halide acid gas. Also, in many applications, preconditioning must be done off-line so that critical downstream components are not compromised by the initial presence of moisture from the purifier.

Aluminosilicate zeolites, particularly molecular sieves of the zeolite A family such as 3A, 4A andzeolite 5A is a well known hygroscopic agent. However, zeolite a molecular sieves have proven unsuitable for use in drying acid gases such as HCl and HBr. See, for example, Barrer, r.m. and Kanellopoulos, a.g., 1970, "adsorption of aluminum chloride vapor on zeolites, section I, hydrogen chloride and ammonia"J.of the Chem.Soc.(A) The method comprises the following steps 765 (decomposition of the 4A molecular sieve was observed after exposure to hydrogen chloride at a pressure of 228mm Hg at 50 ℃ for 18 hours). It has been found that the stability of aluminosilicate zeolites to hydrogen chloride is related to the silica to alumina ratio. The higher the silica to alumina ratio, the more stable the zeolite is to hydrogen chloride, and zeolites having a silica to alumina ratio of 10 or more are considered to have sufficient stability to HCl. In contrast, zeolites of type a and X (synthetic faujasite) having a silica to alumina ratio of 2 and 2.5, respectively, do not provide sufficient stability to hydrogen chloride.

One zeolite with a high silica to alumina ratio for acid gas moisture removal is AW-300 molecular sieve, available from UOP. AW-300 is a natural mordenite-type zeolite having the structureM₂O.Al₂O₃.10SiO₂.6H₂O, M is an alkali metal such as Na; the Si/Al ratio was 10 and the pore diameter was 4 angstroms. Mordenite of this type has been reported to be useful for removing moisture from gaseous mixtures containing hydrogen chloride, such as reformer recycle hydrogen, flue gas, chloroform, trichloroethylene, vinyl chloride and chlorine (Collins, J.J., "one report on acid resistant molecular sieves AW-300 and AW-500", molecular sieves products data sheet, Union Carbide International Co., 270 ParkAvenue, New York, N.Y.10017). Regeneration of the zeolite is carried out by flushing the desorbed moisture with hot gas at 300-. In the same way, see also "method for dehydrating butadiene-hydrogen chloride mixture", Japanese Kokai 7789602 (Cl. C07C11/16)1977, 7-27 (see CA 87:202855 q)]. It has also been reported that activated synthetic mordenite can be used to dry hydrogen chloride: "purification of acid gases with synthetic mordenite", Japanese Kokai Tokkyo koho JP 6154235 [ 8654235 ]][ see CA 105:8642t](ii) a "Zeolite for purification of chlorine gas or hydrogen chloride for semiconductor", Japanese Kokai 7765194 (Cl. C01B7/02), 1977, 5-30 (see CA:87:103913 a)]。

Acid-resistant mordenite-type zeolites such as AW300 is advantageous over chlorosilylated alumina purifiers because its zeolite structure contains independent tetrahedral AlO present in a tetrahedral silica matrix₂The unit can stably inhibit alumina exudation. These units produce a water absorption level that is related to the ion exchange properties and capacity of the zeolite. In contrast, chlorosilylated alumina is octahedral and Al-O-Al bonds, which are more susceptible to reaction and destruction by acidic gases.

Although high silica mordenites have advantages over chlorosilylated alumina, they are not without their drawbacks. Chlorosilylated alumina is purified by irreversible chemical reaction of surface chlorosilyl groups with water, whereas high silica mordenite is mainly purified by reversible physical adsorption of water. As a result, only small amounts of water can be removed from the gas during high silica mordenite purification before significant water desorption occurs. In addition, since physical adsorption is less effective at dehydrating than chemical reactions, high silica mordenite is less effective than chlorosilylated alumina under parallel conditions.

Although high silica mordenite does not have the alumina leaching problem of chlorosilylated alumina, these zeolites often produce unacceptable levels of metal impurities when exposed to acid gases. These undesirable metal emissions are not a significant problem for synthetic mordenites having low metal impurities, particularly low titanium (Ti) levels. However, these zeolites still require preconditioning, including high temperature treatment with acid gases at high pressures (600 psi in the case of HCl and 300psi in the case of HBr) to ensure complete removal of metal contaminants such as magnesium (Mg) and iron (Fe). This preconditioning step causes partial destruction of the zeolite, resulting in loss of purification capacity, formation of silicon halide and simultaneous inter-reaction to form water according to the formula:

wherein X represents halogen, [ SiO ]₂]Represents a zeolite with a high silica to alumina ratio.

Accordingly, there is a need in the art for an acid resistant zeolitic material that is capable of removing trace water from acid gases to very low levels without producing unacceptable levels of metal impurities upon exposure to the acid gas and without requiring a moisture-producing and expensive preconditioning step for removal of metal contaminants. In addition, there is a need in the art for a zeolite that is suitable for removing trace amounts of moisture from acid gases in low pressure and in full cylinder pressure applications.

Other methods of removing water contamination from acid gases that do not rely on zeolites have also been reported. For example, U.S. patent No. 4844719 to Toyomoto et al discloses a method of drying an aqueous gas such as hydrogen chloride by contacting the gas with one side of a permeable polymer made of a fluorine-type copolymer and contacting or reducing the pressure of a dry cleaning gas with the other side of the membrane to thereby remove water from the gas.

U.S. Pat. No. 4925646 to Tom et al discloses a process for drying gaseous hydrogen halides such as HCl, HBr, HF or HI. The process includes contacting a gaseous hydrogen halide with an alkylation precursor composition that includes a metal alkyl compound dispersed throughout a support and/or a metal alkyl co-functional group covalently bonded to a support. The gaseous hydrogen halide reacts with the metal alkyl to form a scavenger composition comprising the corresponding metal halide. The process further comprises contacting the scavenger composition with gaseous hydrogen halide containing water impurities to react the metal halide with the water impurities to produce the corresponding metal halide hydrate and/or oxide and recovering substantially anhydrous gaseous hydrogen halide having a water concentration of less than 0.1ppm by volume.

U.S. patent No. 4564509 to Shealy et al discloses removing oxygen, water vapor and other oxygen-carrying gases from a reactant gas by bubbling the reactant gas through a liquid-phase ternary melt of gallium-indium and an active scavenging agent selected from calcium, lithium, aluminum or magnesium. Oxygen in the gas reacts with the active scavenging agent to form an oxide. The process can be used to remove oxygen and moisture from hydrogen chloride.

U.S. patent No. 4663052 to Sherman et al discloses the use of chabazite containing potassium, rubidium or cesium cations in a process for drying "acid gas streams" such as reformer recycle hydrogen, flue gas, chloroform, trichloroethylene, vinyl chloride, chlorine and generated hydrogen containing the acidic component HCl (paragraph 5, lines 5-17). The Sherman et al chabazite adsorbent is activated in the presence of air or other gas at a temperature of 100 deg.C or above, preferably 200 to 600 deg.C (paragraph 5, lines 51-58).

However, these methods can result in contamination of the gas with other impurities such as oxides or metals. Furthermore, these methods are generally not suitable for large scale semiconductor production practices.

Thus, there is a need in the art for materials that remove trace amounts of moisture from acid gases and that are not susceptible to reaction with acid gases, particularly resistance to aluminum bleed-out and physical degradation. Also, there is a need in the art for a hygroscopic material that can remove trace amounts of moisture from acid gases without the need for a time consuming, expensive preconditioning step with the acid gas during which water is initially produced with a concomitant increase in temperature.

Brief summary of the invention

The invention comprises a process for removing moisture from a gas, particularly from an acidic gas such as hydrogen chloride or hydrogen bromide, comprising contacting the gas with a zeolite having a high silica to alumina ratio, wherein the zeolite has been heated to a temperature above 650 ℃ prior to contact with the gas. Preferably, this heating is sufficient to remove an amount of water from the zeolite (believed to result from dehydroxylation of the zeolite), but insufficient to cause chemical and physical destruction of the zeolite.

The invention also relates to a method of removing moisture from a gas comprising heating a zeolite (said zeolite having a high silica to alumina ratio) to a temperature of about 400 ℃ for a time sufficient to desorb a first portion of water physically adsorbed onto the zeolite, followed by heating the zeolite to a temperature above about 650 ℃ for a time sufficient to remove a second portion of water (believed to result from dehydroxylation of the zeolite) to form a superheated zeolite, and subsequently contacting the superheated zeolite with the gas and allowing the superheated zeolite to adsorb water from the gas.

The invention also relates to a superheated zeolite which has been heated to a temperature above about 650 ℃ sufficient to remove an amount of moisture from the zeolite (it is believed that the removal of moisture from the zeolite is by dehydroxylation), wherein the superheated zeolite has a high silica to alumina ratio and a low metal content.

The invention also relates to a process for preparing a dehydroxylated zeolite comprising heating a zeolite to a temperature of about 400 ℃ for a time sufficient to desorb a first portion of water physically adsorbed on the zeolite, followed by heating the zeolite to a temperature greater than about 650 ℃ for a time sufficient to remove a second portion of water from the zeolite by dehydroxylation of the zeolite.

Brief description of the drawings

FIG. 1: thermogravimetric analysis (TGA) scan of a sample of mordenite produced by Tosoh in japan 65.9 mg. The TGA scan was performed as described in example 1 (A).

FIG. 2: TGA scan of a 64.7mg sample of Tosoh mordenite. The TGA scan results indicate main H₂The center of the O desorption (weight loss) peak was at 140 ℃ and the center of the second peak was at about 890 ℃. The TGA scan was performed as described in example 1 (B).

FIG. 3: a TGA scan of a 68.7mg sample of United Catalysts (UC) mordenite heated to 800 ℃. The TGA scan shows the major low temperature water peak and two high temperature peaks at about 580 ℃ and about 800 ℃. The TGA scan was performed as described in example 1 (C).

FIG. 4: TGA scan of a 66.6mg sample of Tosoh mordenite. The TGA scan shows that the sample loses about 3.5 wt% water at low temperature (peak at 130 ℃) and about 0.3 wt% water at about 800 ℃. The TGA scan was performed as described in example 1 (D).

FIG. 5: TGA scan of a 66.6mg Tosoh mordenite sample showed that the low and high temperature water peaks of Tosoh mordenite appeared when heated to 400 ℃ and 800 ℃. The TGA scan was performed as described in example 1 (E).

FIG. 6: TGA scans of 119.3mg samples of United Catalyst (UC) mordenite heated in stages to 400 ℃ and 700 ℃. The TGA scan results show more water loss at elevated temperatures, i.e., the sample is about 1.3% dehydrated. The TGA scan was performed as described in example 1 (F).

FIG. 7: TGA scans of 245.4mg of a sample of United Catalyst (UC) mordenite heated in stages to 350 ℃ and 700 ℃. The TGA scan was performed as described in example 1 (G).

FIG. 8: TGA scan results of a rerun of 245.4mg of the fig. 7 sample (example 1(G)) after re-dehydrating the sample under ambient conditions (about 25% humidity). The TGA scan shows significantly less high temperature water is desorbed. The TGA scan was performed as described in example 1 (H).

FIG. 9: TGA scan results of heating a 329.2mg sample of Tosoh mordenite in stages. The TGA scan was performed as described in example 1 (I).

FIG. 10: TGA scan of a 69.0mg PQ mordenite sample heated in stages to 400 ℃ and 700 ℃. The TGA scan shows that about 15% weight loss occurs at the second temperature ramp. The TGA scan was performed as described in example 1 (J).

FIG. 11: repetition of the TGA scan of figure 10 (example 1 (J)). The TGA scan indicates a weight loss at elevated temperatures of about one third of the previous weight loss. The TGA scan was performed as described in example 1 (J).

FIG. 12: the TGA scan as shown in FIG. 11, performed as described in example 1(J), was repeated. Repeated TGA scans gave essentially the same results.

FIG. 13: the TGA scan as shown in FIG. 12, performed as described in example 1(J), was repeated. Repeated TGA scans gave essentially the same results.

FIG. 14: the TGA scan as shown in FIG. 13, performed as described in example 1(J), was repeated. Repeated TGA scans gave essentially the same results. The TGA scans of figures 10, 11, 12 and 13 show excellent reproducibility in the removal of water from the calcined-rehydrated mordenite. About half of the percent weight loss occurs above 400 ℃ (about 5% of the total weight loss).

Figure 15 TGA scan of 46.1mg of PQ mordenite β heated in stages to 400 ℃ and 700 ℃ the TGA scan shows a 5.2mg weight loss (11% by weight of the sample) during the first temperature ramp and a 0.3mg weight loss (0.5% by weight of the sample) during the second temperature ramp, the TGA scan was performed as described in example 1 (K).

FIG. 16: TGA scan of PQ-type Y zeolite samples heated in stages to 400 ℃ and 700 ℃. The TGA scan indicates that a weight loss of about 0.5% occurs at the second temperature ramp. The PQ-type Y zeolite has substantially similar characteristics as mordenite. The TGA scan was performed as described in example 1 (L).

FIG. 17: TGA scan of 73.8mg PQ ZSM-5 samples heated in stages to 400 ℃ and 700 ℃. The TGA scan shows that about 5.0mg weight loss (about 6.5% of the sample weight) occurs at the first temperature ramp and about 0.3mg weight loss (about 0.4% of the sample weight) occurs at the second temperature ramp. The TGA scan was performed as described in example 1 (M).

FIG. 18: a graphical representation of the effect of gas pressure (psia) on the water capacity (L/L) of dehydroxylated mordenite is described in example 4. The graph shows the effect of pressure on the water uptake of the purification agent and the use of high pressure matrix gas can greatly increase the purification agent capacity.

Detailed description of the invention

The present invention relates to a process for removing trace amounts of moisture from acid gases comprising contacting the gas with a zeolite having a high silica to alumina ratio, wherein the zeolite has been heated to a temperature above about 650 ℃. The term "superheated," as used herein to describe the present invention and zeolites useful in the process of the present invention, means that the zeolite is heated to a temperature of about 650 ℃ or above. This heating is believed to cause dehydroxylation of the zeolite. We have found that superheated zeolites have the ability to effectively absorb moisture from acid gases such as hydrogen chloride or hydrogen bromide to levels below 0.1ppm without the dealumination problems of chlorosilylated alumina. In addition, the superheated zeolite used in the process of the present invention does not require a preconditioning step with the acid gas to be purified that is costly, inconvenient, and moisture producing. Thus, the present invention eliminates the problem of initial moisture generation associated with chlorosilylated alumina and conventional zeolite purifiers.

The invention also relates to a process for preparing a dehydroxylated zeolite comprising heating a zeolite at a temperature of about 400 ℃ for a time sufficient to desorb a first portion of water physically adsorbed on the zeolite, followed by heating the zeolite at a temperature above about 650 ℃ for a time sufficient to remove a second portion of water by means of dehydroxylation of the zeolite.

The invention also relates to a superheated zeolite comprising a mordenite-type zeolite heated to a temperature above about 650 ℃ to a temperature sufficient to remove moisture from an amount of the zeolite by dehydroxylation, wherein said superheated zeolite has a high silica to alumina ratio and a low metal content.

The invention also relates to a dehydroxylated zeolite which has been heated at a temperature of about 400 ℃ for a time sufficient to desorb a first portion of the water physically adsorbed on the zeolite and at a temperature above about 650 ℃ for a time sufficient to remove a second portion of the water by virtue of dehydroxylation of the zeolite, wherein the zeolite has a high silica to alumina ratio and a low metal content.

The zeolite of the present invention should have low levels of iron, titanium and magnesium. Preferably, the zeolite of the present invention has less than about 20ppm titanium, less than about 100ppm iron, and less than about 11ppm magnesium. Further, it is preferred that the zeolite of the present invention have less than about 1% by weight Na₂Sodium in terms of O.

Conventional zeolite purifiers used to remove moisture from acid gases, such as mordenite, are typically activated at temperatures of 300-. At such temperatures virtually all physically adsorbed water is removed by desorption. Calcination of the mordenite purifying agent is typically carried out at higher temperatures up to 650 ℃ without additional moisture loss. However, if the mordenite is subjected to temperatures above 650 ℃ (i.e. superheated), another portion of the water is liberated, believed to be due to dehydroxylation reactions involving the two hydroxyl groups of the two acidic zeolite forms (H-M) per water molecule. This is the edge of the thermal stability of the zeolite beyond which the microporous structure of the zeolite collapses. However, if the superheated mordenite is not left at the superheated temperature for a longer period of time, the superheated mordenite is quite stable.

The high silica alumina ratio mordenite of the acidic zeolite form (H-M) is a strong Bronsted acid. By dehydroxylation under superheated conditions, the bronsted acid sites are converted to very hygroscopic lewis acid sites according to the formula:

dehydroxylated mordenites have been known for more than twenty years: kuhl, G.H., 1977, "acidic" molecular sieves of mordenite-II, James R.Katzer eds., ACS Symposium Series40, Chapter 9, pp.96-107. Kuhl discloses dehydroxylation of mordenite by heating the zeolite at a rate of 5 ℃ per minute at a temperature range of 525-. However, the Kuhl method does not mention the phenomenon known as "steaming" (where physically adsorbed water reacts with the zeolite at temperatures above 400 ℃ upon desorption to chemically modify the zeolite and reduce its hygroscopic effectiveness). The process for preparing the dehydroxylated zeolites of the present invention avoids the problem of steaming by maintaining the zeolite at a temperature of about 400 ℃ for a time sufficient to remove all of the physically adsorbed water. At temperatures of about 400 c or below, the physically adsorbed water does not react with the zeolite and the problem of steaming is avoided. Furthermore, Kuhl does not describe dehydroxylated zeolites with low metal content.

We have unexpectedly found that dehydroxylated mordenite has the ability to effectively adsorb moisture from an acidic gas stream. The present invention combines the high effectiveness of strong lewis acids in removing moisture with the high capacity of dehydroxylated mordenite for chemical water to provide acid resistant zeolites having superior purification performance. The inventors also believe that the effective removal of surface hydroxyl groups greatly reduces the water reaction with acidic gases (e.g., HCl, HBr) at low temperatures according to the following formula:

wherein X represents a halide and [ Zeo ] represents a zeolite.

Preferred zeolites of the present invention are mordenite-type zeolites. In a preferred embodiment, the zeolite has a silica to alumina ratio of about 10 to 30; particularly preferred are zeolites having a silica to alumina ratio of about 15 to 20. Other H-type (i.e., acidic) zeolites having a high silica to alumina ratio may also be used in the process of the present invention.

The zeolite used in the present invention can have various particle sizes. For example, zeolites having particle sizes in the range of 1 to 10mm may be used. Further, the zeolite used in the present invention may comprise a mixture of different particle sizes, or may have a substantially uniform particle size. Preferably, the zeolite used in the present invention has a uniform particle size of about 1 to 1.5mm (i.e., about 1/16 inches). More preferably, the zeolite used in the present invention is a uniform spherical bead having a particle size of about 1-1.5 mm. Alternatively, the zeolite may be in the form of cylindrical particles. Preferably the cylindrical particles have a height of about 1-1.5mm and a cross-sectional diameter of about 1-1.5 mm; but mixtures of different particle sizes may also be used.

Examples of mordenite-type zeolites useful in the present invention include T-2581 heterogeneous catalysts available from United catalysts, Inc. Louisville, KY and mordenite CBV 20A available from Zeolyst International Products, Valley Forge, PA examples of zeolites other than mordenite which may be used in the process of the present invention are high silica to alumina ratio ZSM-5(MFI), ZSM-11(MEL), β (BEA), faujasite USY (FAU), hexagonal (hexagonal) faujasite (also known as BSS EMT), Ferrierite (FER) and Chabazite (CHA).

Preferably the zeolites of the invention have low levels of metal impurities. It is particularly preferred that the zeolite has a low titanium (Ti) and iron (Fe) content. Preferred zeolites for use in the process of the present invention are synthetic mordenites having a low metal content; however, natural mordenite zeolites may also be used. A particularly preferred zeolite is high metal purity mordenite ("Tosoh zeolite") available from Tosoh, inc. Such low metal mordenite is commercially available from Tosoh USA, 1100 Circle 75 Parkway, Suite 600, Atlanta, GA 30339, under the supplier code "H-mordenite". This zeolite is a synthetic mordenite-type zeolite having a silica to alumina ratio of about 15 and containing about 20% silica binder (the final silica to alumina ratio being about 19). Tosoh zeolite is particularly preferred because it has a low titanium impurity level (i.e., less than about 20ppm titanium). The Tosoh zeolite also has very low iron and magnesium contents (below about 100ppm and about 11ppm, respectively).

The total amount of water (i.e., "chemical water") removed by dehydroxylation of the Tosoh zeolite is 0.5 to 0.6 wt.% of the zeolite. This corresponds to the removal of about 6 litres of water vapour per litre of zeolite by dehydroxylation at standard temperature and pressure ("s.t.p."). Thus, in contrast to mordenite activated at lower temperatures, dehydroxylated Tosoh zeolite has the ability to additionally reabsorb water vapour in about 6 litres of the gas stream. The total amount of physically adsorbed water removed by heating the zeolite to about 400 c was about 14 liters of water vapor (at standard temperature and pressure) per liter of zeolite. This increases the total water capacity measured at normal pressure (for example by the fourier infrared method) to a value higher than the capacity of chemical water obtained by dehydroxylation. Therefore, a dewatering capacity of about 20 liters (s.t.p.) per liter can be achieved using the superheated zeolite according to the invention. However, the additional capacity for physical water adsorption comes at the cost of a potential reduction in purification effectiveness to some extent. Thus, while zeolites activated at conventional temperatures (i.e., about 400 ℃) have the ability to physisorb only about 14 liters of water vapor (s.t.p.), zeolites activated according to the present method have the ability to sorb about 20 liters of water vapor through a combination of "chemical" and physisorption.

The superheating of the zeolite is carried out at a temperature above about 650 c but below the collapse of the zeolite micropores. In the case of Tosoh zeolites, pore collapse occurs at temperatures above 900 ℃. However, the upper limit of the degree of heating depends on the type of zeolite and the structure of its micropores. The zeolite may be held at a temperature of 650 ℃ or above for a time sufficient to dehydroxylate a sufficient amount of chemical water from the zeolite sample. Preferably, the zeolite of the present invention is maintained at elevated temperatures for about one hour, but not more than about 6 to 8 hours to reduce structural damage that can lead to reduced water capacity. Preferably to ambient temperature under a moisture-free atmosphere (e.g. in Nanochem) before contacting the zeolite with the gas to be purified^®-under a purified nitrogen atmosphere); but may also be such that the zeolite still has a certain heat, e.g. about 300 c, toAt a lower temperature.

The process of the present invention can be used to remove moisture from almost any non-alkaline gas; however, the present invention is particularly useful for purifying acidic gases including hydrogen chloride and hydrogen bromide from acidic gases that appear to be free of other effective purifying agents [ particularly HBr at cylinder pressures (about 320 psi;HCl about 620psi]Removing trace water. The process of the present invention is also applicable from a wide variety of gases used in the semiconductor industry (including halide gases such as chlorine, boron trichloride, boron trifluoride, nitrogen trifluoride, sulfur hexafluoride, silanes (particularly chlorosilanes), silicon tetrachloride, silicon tetrafluoride, tungsten hexafluoride, carbon tetrafluoride and phosphorus pentafluoride); other chemicals used in the semiconductor industry such as hydrogen fluoride; hydride gases such as arsine (AsH)₃) Phosphine (PH)₃) And Silane (SiH)₄) (ii) a And bulk gases such as nitrogen (N)₂) Oxygen (O)₂) Hydrogen (H)₂) Carbon dioxide (CO)₂) Argon (Ar) and helium (He) remove moisture.

Examples

Example 1: thermogravimetric analysis (TGA) of zeolites

Example 1(A)

65.900mg of a zeolite sample (lot: HSZ-640H0D, Z-951201, particle diameter 1.5mm, bulk density 0.58g/ml, crushing strength (aqueous) 0.22kg/mmL, surface area (Langmuir) 490m produced by Tosoh, Japan (Lot: HSZ-640H0D, Z-951201)²Per g, cylindrical pellets with a cross-sectional diameter of 1 to 1.5 mm) are simply flushed with nitrogen. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer TGA-7 thermogravimetric analyzer. The sample was heated to 35 ℃ and held for one minute. The temperature was then raised to 400 ℃ at a rate of 20 ℃ per minute and held at 400 ℃ for one hour, during which time substantially all (about 5mg) of the physically adsorbed water was removed from the sample. The temperature was then raised to 700 c at a rate of 20c per minute and held at 700 c for about one hour. During which time water equivalent to 0.245mg or equivalent to 0.37% by weight of the sample was lost. After correction for buoyancy and airflow and density effects, the high temperature water loss was about 0.35mg (about 0.50% by weight).

In total, 94% of the desorbed water from the sample was desorbed by a physical desorption method at 400 ℃ and 6% of the desorbed water was desorbed by a chemical method of dehydroxylation at 700 ℃. The TGA profile of this experiment is shown in figure 1.

The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes. Once cooled to 200 ℃, the sample reabsorbed water from the surroundings through a rehydroxylation mechanism. The sample was then cooled to 25 ℃ at a rate of 20 ℃ per minute. After cooling to ambient temperature, the sample reabsorbed additional water by physical re-absorption. The entire experiment was repeated to reach the same conclusion. The reproducibility of the experiment obtained with the same sample indicates that the zeolite remains as such or substantially as such.

When superheated above 900 ℃, the zeolite is destroyed and no re-adsorption of water by rehydroxylation or physisorption occurs. Subsequent TGA experiments with the samples gave a flat curve without weight loss.

Example 1(B)

TGA scans of 64.7mg Tosoh zeolite samples were performed as follows. The sample was held at 25 ℃ for 1 minute. The sample was then heated from 25 ℃ to 1200 ℃ at a rate of 40 ℃ per minute. The TGA curve is shown in figure 2. TGA scans indicated main H₂The O desorption (weight loss) peak was centered at 140 ℃ and the second peak was centered at about 890 ℃.

Example 1(C)

TGA scans of 68.7mg of United Catalysts (UC) mordenite T-2581 heterogeneous catalyst (25-35% alumina; 65-75% mordenite; < 5% nickel oxide; 30-40 lbs/cubic foot bulk density) were conducted as follows. The sample was held at 35 ℃ for 1 minute. Then raised to 800 c at a rate of 20 c/min and held at 800 c for 1 hour. The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes, then cooled to 50 ℃ at a rate of 20 ℃ per minute. The TGA profile of this experiment is shown in figure 3. The TGA scan shows a main low temperature water peak and two high temperature peaks at about 580 ℃ and about 800 ℃.

Example 1(D)

TGA scans of 66.6mg of Tosoh zeolite were performed as follows. The sample was held at 35 ℃ for 1 minute. Then raised to 800 c at a rate of 20 c/min and held at 800 c for 1 hour. The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes, then cooled to 50 ℃ at a rate of 20 ℃ per minute. The TGA profile of this experiment is shown in figure 4. The TGA scan shows that the amount of water lost from the sample at low temperatures (peak at 130 ℃) is about 3.5% by weight of the sample and the amount of water lost at about 800 ℃ is about 0.3% by weight of the sample.

Example 1(E)

TGA scans of 66.6mg of Tosoh zeolite were performed as follows. The sample was held at 35 ℃ for 1 minute. Then ramped up to 400 c at a rate of 20 c/min and held at 400 c for 1 hour. The temperature was then raised to 800 ℃ at a rate of 20 ℃ per minute. The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes, then cooled to 25 ℃ at a rate of 20 ℃ per minute. The TGA profile of this experiment is shown in figure 5. TGA scans show low and high temperature water peaks.

Example 1(F)

TGA scans of 119.3mg United Catalysts (UC) mordenite T-2581 (identical to example 1 (C)) were performed as follows. The sample was held at 35 ℃ for 1 minute. Then ramped up to 400 c at a rate of 20 c/min and held at 400 c for 1 hour. The temperature was then raised to 700 ℃ at a rate of 20 ℃ per minute and held at 700 ℃ for 1 hour. The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes, then cooled to 25 ℃ at a rate of 20 ℃ per minute. The TGA profile of this example is shown in FIG. 6. TGA scans showed that more water was lost at high temperature, i.e. about 1.3% of the dehydrated sample.

Example 1(G)

A TGA scan of 245.4mg of United Catalysts (UC) mordenite T-2581 (identical to example 1 (C)) was performed as follows. The sample was held at 35 ℃ for 1 minute. Then raised to 350 c at a rate of 20 c/min and held at 350 c for 1 hour. The temperature was then further raised to 700 ℃ at a rate of 20 ℃ per minute and held at 700 ℃ for 1 hour. The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes, then further cooled to 25 ℃ at a rate of 20 ℃ per minute. The TGA profile of this experiment is shown in figure 7.

Example 1(H)

The sample was rehydrated at ambient conditions (approximately 5% humidity) and then subjected to repeated TGA scans of 245.4mg of a United Catalysts (UC) mordenite sample from example 1 (G). TGA scans were performed as described in example 1 (G). The TGA profile of this experiment is shown in figure 8. TGA scans showed a significant reduction in water desorbed at high temperatures.

Example 1(I)

TGA scans of 392.2mg of Tosoh zeolite were performed as follows. The sample was held at 35 ℃ for 1 minute. The temperature was then raised to 400 ℃ at a rate of 20 ℃/min and held at 400 ℃ for 240 minutes. The temperature was then further raised to 700 ℃ at a rate of 20 ℃ per minute and held at 700 ℃ for 1 hour. The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes, then further cooled to 25 ℃ at a rate of 20 ℃ per minute. The TGA scan curve of this experiment is shown in figure 9.

Example 1(J)

69.0mg of PQ Corporation mordenite (Zeolyst International product, code CBV 20A, silica to alumina ratio 20; nominal cationic form: ammonium; 0.08 wt% Na)₂O；500m²Surface area/g). The sample was held at 35 ℃ for 1 minute. The temperature was then raised to 400 ℃ at a rate of 20 ℃/min and held at 400 ℃ for 1 hour. The temperature was then further raised to 700 ℃ at a rate of 20 ℃ per minute and held at 700 ℃ for 1 hour. The sample was then cooled to 200 ℃ at a rate of 20 ℃ per minute and held at 200 ℃ for 30 minutes, then further cooled to 50 ℃ at a rate of 20 ℃ per minute. The TGA profile of this experiment is shown in figure 10. The TGA scan shows that about 15% weight loss occurs in the second temperature ramp. TGA scans were repeated using the same conditions and using the same samples. A repeated TGA scan of this sample is shown in figure 11, which indicates a weight loss at elevated temperatures of about one third of the previous. TGA scans were repeated three more times under the same conditions. The TGA curves of these repeated TGA scans are shown in figures 12, 13 and 14, respectively, which show essentially the same results. These TGA scans confirm that the reproducibility of dehydration from calcined rehydrated mordenite is excellent. About half of the percent weight loss occurs above 400 ℃ (about 5% of the total weight loss).

Example 1(K)

46.1mg PQ was performed using the same temperature program as described in example 1(J)Zeolite type β (BEA) Corporation (Zeolyst International Product, code No. CP814B, silica to alumina ratio 20; nominal cationic form: ammonium; 0.05 wt.% Na)₂O；680m²/gSurface area). The TGA profile of this experiment is shown in figure 15. The TGA scan shows that a 5.2mg weight loss occurs in the first temperature ramp (11% sample weight) and a 0.3mg weight loss occurs in the second temperature ramp (0.5% sample weight).

Example 1(L)

Zeolite Y type PQ Corporation (FAU) (Zeolyst International Product, code CBV 712; silica to alumina molar ratio 12; nominal cationic form: ammonium; 0.05 wt.% Na, was carried out using the same temperature procedure as described in example 1(J)₂O; 24.35 angstrom units pore size; 730m²Surface area/g). The TGA profile of this experiment is shown in figure 16. The TGA scan indicates that a weight loss of about 0.5% occurs in the second temperature ramp and that the PQ-type Y zeolite has essentially the same properties as mordenite.

Example 1(M)

73.8mg of a PQ corporation ZSM-5 type zeolite (Zeolyst International Product, code CBV 3024; silica to alumina molar ratio 30; nominal cationic form: ammonium; 0.05 wt.% Na) were carried out using the same temperature program as described in example 1(J)₂O；375m²Surface area/g). The TGA profile of this experiment is shown in figure 17. The TGA scan shows that a 5.0mg weight loss occurs in the first temperature ramp (6.5% of the sample weight) and a 0.3mg weight loss occurs in the second temperature ramp (0.4% of the sample weight).

Example 2: preparation of 1L Scale superheated Zeolite by activation of Tosoh mordenite

Example 2(A)

637.3 grams (about 1.05 liters) of freshly sieved Tosoh mordenite (8 to 25 mesh) were loaded into a quartz reactor tube (2 inch inner diameter).

The reactor was fitted with a quartz frit to hold the solid particles in a down-flow direction. A small hole in the middle of the frit was used to introduce the thermocouple into the reactor (upstream), eventually with the tip of the thermocouple slightly more or less locatedIn the middle of the zeolite bed. At the other end of the reactor, a pyrex glass vessel was connected to the reactor mouth by a wide mouth glass fitting. Before and during activation, the container was constantly heated by an external heating belt to about 130 ℃ to eliminate moisture from the glass. During the activation process, the reactor-vessel was continuously used and passed through Nanochem^®Nitrogen gas from dry cylinders purified by purifiers or nitrogen flushing plant to further remove waterThe fractions are reduced to a level of about 1ppm to about 100ppt or less. The nitrogen purge gas was flowed into the system through a valved side arm connected to the upstream portion of the reactor near the wide mouth of the reactor. At the downstream end, nitrogen can be fed to a second Nanochem through a side pipe^®Purifiers (to prevent re-entry of cooling stage water into the reactor) or through a bypass line and then discharged through a rotameter (1-5 liters per minute). The purge flow rate is maintained at a level of 1-2 liters per minute, typically about 1.5 liters. Initially, nitrogen was vented through a bypass line during heating. The reactor was placed in a tubular horizontal Lindberg high temperature (0-1200 c) furnace.

Heating of the reactor is started by setting temperature control to obtain a bed temperature of more than 200 ℃; sufficient time is allowed for the internal and external temperatures (as measured by a second thermocouple placed between the reactor tube and the furnace ceramic material) to become virtually the same or very close. When the external temperature was 249 ℃ and the internal temperature was 223 ℃, water was observed to condense at the cold reactor outlet. The droplets formed were evaporated into the air stream using an air heating gun. The temperature was then raised to 280 ℃ (inside and outside) when more condensed water was observed; however, these droplets in the outlet portion of the reactor eventually disappear. The flow rate was 1.0 liter per minute. Heating was continued to a temperature of 400 ℃ and then to a temperature of 445 ℃ (inner). At this point the nitrogen flow was increased to 2 litres per minute to help remove the water produced at the reactor outlet due to extensive dehydration of the zeolite. Subsequently, the temperature was increased to about 740 ℃ over a period of about 2 hours. After about 30 minutes at 740 ℃, the heating was stopped. The nitrogen flow was bypassed to a second Nanochem^®Purifier (by closing the idle line and opening the purifier valve)And continued overnight while the system was slowly cooled back to room temperature. The glass container is then heated further.

After cooling overnight, the heating tape was removed from the vessel and the reactor-vessel unit was disconnected from the gas line while still maintaining access to the outside air, and the purifier was shut down. The reactor-vessel was carefully removed from the furnace and the zeolite was transferred into the vessel by tilting it to a vertical position. The reactor-vessel was then transferred to a reactor using Nanochem^®Purified nitrogen purged sealed plastic encasement. The plug fitted to the wide mouth of the container, which had been heated in an oven at 110 ℃ for 24 hours, was placed in a plastic sleeve. The dry nitrogen purge of the plastic sheath was sufficient to slightly expand the plastic sheath. After 2.5 hours in the plastic sheath, the vessel and the reactor were separated (in the plastic sheath) and immediately plugged with a stopper. The nitrogen purge was stopped and the vessel (separated from the reactor) was transferred to Nanochem^®Purification ofIn a glove box under nitrogen. In the glove box, the contents of the pyrex container were transferred to a polypropylene jar that had been previously stored in the glove box at least overnight to remove moisture from the plastic. The pyrex container is then returned to the reactor unit for production of the next batch of product.

Example 2(B)

The procedure of example 2 was repeated except that this time 620 g of Tosoh zeolite was treated and the heat treatment was carried out at 700 c for 105 minutes.

Example 2(C)

Another batch of 1 liter of purification agent was prepared, but 650 grams (about 1.1 liter) of zeolite from another newly opened feed drum was used, as it contained no visible dust/dust and did not need sieving. The activation of the zeolite under superheated conditions was carried out at 705 c for 120 minutes.

Example 2(D)

This is a reference experiment for heat-activated purifiers without overheating. The experiment was carried out essentially as in example 2(A) except for the superheating. 635 grams of Tosoh zeolite from the same drum as example 3 was charged to the reactor. The mixture was heated at 415 ℃ for 7 hours.

Example 3: determination of the Water Capacity of superheated zeolites Using Fourier Infrared (FT-IR)

The moisture capacity of the superheated zeolite samples prepared as described in example 2(A) above was determined using Fourier transform Infrared (FT-IR) Spectroscopy as described in D.E. Pivonka in Applied Spectroscopy, Vol.45, vol.4, 597, page 603, 1991.

The instrument used was a Nicolet Magna760 FT-IR photometer equipped with an MCT (Mercury cadmium tellurium alloy) detector. The photometer was fitted with a 10cm stainless steel cell for an auxiliary sample chamber for measuring water concentration at the purifier inlet and a 10cm nickel plated stainless steel cell for measuring water concentration downstream of the purifier, as described by Pivonka. The inlet gas stream to the purifier, referred to herein as "wet-on-demand", has a water concentration in the range of several hundred to several thousand ppm. The water concentration of the gas downstream of the purifier prior to breakthrough is typically in the range of 100ppb to 10 ppm. The spectrometer device was enclosed in a 20 liter per minute constant Nanochem^®Purified nitrogen purge flows down the dried plastic box.

The "wet on demand" gas stream having a constant concentration of about 400-500ppm was generated as follows. Nitrogen gas was passed through a water diffusion vial in a stainless steel autoclave maintained at a constant temperature of 80 ℃ to produceAn aqueous nitrogen stream. The aqueous nitrogen stream is passed through a dry matrix stream (i.e., N)₂HCl or HBr) to produce a "wet on demand" gas stream. The exact concentration of water in the moisture-required gas stream was calculated from the gas flow rate (via calibrated mass flow controllers) and the amount of water in the diffusion vial before and after the test. The purifier unit comprises an L-60 vessel with 60ml of purifier material in a tubular 20cm high bed. The "wet on demand" gas stream was introduced into the purifier unit at a flow rate of 2000cc (STP)/min at a pressure of 13.4 psia. The temperature of both the 10cm and 10m FT-IR cells was maintained at 110 deg.C and the MCT detector was maintained at-190 deg.C.

The FT-IR measurement is based on a measurement at 3853cm^-1Change of the lower water absorption line. Continuous automatic and programmed operation of FT-IR by using OMNIC^TMAnd (4) carrying out software. The operation is carried out until a breakthrough phenomenon occurs, i.e. a sudden and sharp increase in the water content downstream of the purifier. Cross-section of the breakthrough point at a baseline (typically below the FTIR detection limit, i.e., about 100ppb) representing total removal of moisture by the purifierAnd tangent definition and calculation of the line of penetration showing a gradual increase in water content (higher intensity absorption). The collected data and breakthrough points were converted by direct arithmetic calculations into capacity expressed as liters of water removed per liter of purifying agent (gas phase). With HCl, HBr and N₂The results of FTIR capacity testing of the matrix gas against the superheated mordenite purifier are shown in Table 1.

The capacity under nitrogen is the lowest, but is still very high and is about 50% (11L/L) higher than the capacity of chlorosilylated alumina measured under the same conditions. The measured 'recording' capacity was 35% higher than under nitrogen under HBr. Possibly because the zeolite creates more sites for moisture removal during acid gas 'conditioning' (perhaps due to chemisorption or chemical reaction). One possibility is partial reaction of the zeolite with HCl and HBr, respectively, to give chlorosilyl and bromosilyl or aluminum alkyl groups (allyl) on the zeolite

T is a tetrahedral framework element (Si or Al) and X is a halide element (Cl, Br).

Example 4: measurement of moisture capacity of superheated zeolites using an Ametek 2850 moisture analyzer

In this example, we illustrate the use of an Ametek 2850 moisture analyzer to measure the moisture capacity of a purification agent. The analyzer can measure 0.1-1000ppm at pressures ranging from 15-75psigA range of moisture. The purifier unit required 400-450ppm moisture in nitrogen, which was generated as described in example 3 by diluting the nitrogen stream through the autoclave containing the diffusion vial (to provide 8000-9000ppm moisture content) with a dry nitrogen stream at a ratio of 1 to 19, respectively. The combined gas stream was passed through the purifier at a rate of 2000cc (STP)/min at a pressure of 29.7 psia. The 'penetration' characteristics were obtained as in the FTIR measurements described in example 3, but the penetration point in this example was defined and calculated as the 1ppm moisture content point on the penetration curve. This point is very close to that defined in the FTIR measurement described in example 3Penetration point (within about 5%). The water content analysis can be converted into Microsoft Excel^®Is performed by the computer program of (1). The collected data and breakthrough points were converted by direct arithmetic calculations into capacity expressed as liters of water removed per liter of purifying agent (gas phase). The results are shown in Table 1.

According to table 1, the Ametek results are actually higher than the FTIR results, which may be due to the difference in pressure. An experiment at 74.7psia appears to confirm that the effect of pressure on the water adsorbed on the purifying agent is considerable. Fig. 18 demonstrates this effect. Thus, the use of high pressure matrix gas may greatly increase the water capacity of the purifying agent. Comparison of different batches of superheated mordenite purifier at the same pressure (29.7psia) showed consistent capacity data of about 30L/L. In contrast, purifiers prepared by activation at 415 ℃ exhibited much lower capacity. Superheating increased the capacity by about 30% as measured by the Ametek capacity.

Example 5: calculation of the moisture Capacity of superheated Tosoh mordenite Using thermogravimetric analysis (TGA)

The effect of superheating of Tosoh mordenite on moisture capacity was calculated based on TGA results determined with a nitrogen base gas. The results are well consistent based on the prediction of TGA and the actual effect obtained with the 1L sample.

As listed in Table 1, a sample of superheated zeolite had a capacity of 17L/L (at atmospheric pressure). A typical TGA experiment as described in example 1(a) and shown in figure 1 provides the following results: 5.9% water loss at 400 deg.C; between 400 ℃ and 700 ℃, there is an additional 0.38% water loss, and 0.50% water loss after correction for buoyancy and flow effects (by subtracting the blank curve of an empty TGA vessel). The initial weight of the partially hydrated mordenite was 65.90 mg. Therefore, 3.89mg of water is removed at 400 ℃ and 0.33mg of water is removed at 700 ℃; the superheated sample weighed 61.68 mg.

As shown in table 1, the capacity of one of the superheated zeolite samples was 17 liters of water vapor per liter of superheated zeolite. 17 litres of water vapour correspond to 13.66 grams of water; one liter of the superheated zeolite weighed 600 grams. Thus, 600 grams of superheated zeolite (1L) had the capacity to adsorb 13.66 grams of water. Therefore, the capacity value corresponds to (13.66/600) × 100 ═ 2.277% by weight. This includes both chemically (rehydroxylation) and physically adsorbed reabsorbed water. Therefore, in the case of the above sample, the total amount of reabsorbed water reaching the capacity breakthrough point was (61.68 × 2.277)/100 — 1.404 mg. Since the 'dehydroxylated' water amount was 0.33mg, it is reasonable to assume that all this water can be reabsorbed, with the physisorbed 'remaining' water being 1.404-0.33-1.074 mg (27.6% of the desorbed water to 400 ℃).

We can now calculate the capacity of the zeolite to activate at 400 ℃ from TGA. On (61.68+0.33) ═ 62.01mg of dried zeolite activated at 400 ℃ 1.074mg of water were again physically adsorbed. Since 1.074mg of water was 1.3365ml of standard gas phase water and since 62.01mg of zeolite purification agent activated at about 400 ℃ had a volume of 0.10335ml, the capacity was 1.3365/0.10335-12.9L/L. The increased capacity due to 'dehydroxylation' was (17-12.9)/12.9-0.315 (or 31.5%), which is well consistent with the results above in the large scale case.

Table 1: moisture capacity of superheated zeolite

Activation temperature (. degree. C.). sup. Time (minutes)	Base gas Body	Pressure (psia)	Analyzer	Moisture capacity (L/L)
Activation temperature (. degree. C.). sup. Time (minutes)	Base gas Body	Pressure (psia)	Analyzer	Moisture capacity (L/L)	740/30 (example 2A)	HCl HBr N₂ N₂	13.4 13.4 13.4 29.7	FTIR FTIR FTIR Ametek	20 23 17 27
700/105 (example 2B)	N₂	29.7	Ametek	31	740/30 (example 2A)	HCl HBr N₂ N₂	13.4 13.4 13.4 29.7	FTIR FTIR FTIR Ametek	20 23 17 27
700/105 (example 2B)	N₂	29.7	Ametek	31	705/120 (example 2C)	N₂ N₂	29.7 74.7	Ametek Ametek	29 52
415/420 (example 2D)	N₂	29.7	Ametek	23	705/120 (example 2C)	N₂ N₂	29.7 74.7	Ametek Ametek	29 52

The scope of the invention is not limited by the specific embodiments and examples described herein. Indeed, those skilled in the art will appreciate from the foregoing description and the accompanying drawings that: there may be variations in addition to the embodiments and examples described herein. Such variations are intended to be within the scope of the appended claims.

Various documents are cited herein, the disclosures of which are incorporated by reference in their entirety.

Claims

1. A method of removing moisture from a gas comprising contacting the gas with a zeolite having a silica to alumina ratio of about 10 or greater, wherein the zeolite has been heated to a temperature of about 650 ℃ or greater prior to contacting with the gas.

2. The process of claim 1 wherein the temperature above 650 ℃ is sufficient to cause dehydroxylation of the zeolite.

3. The process of claim 1 wherein the zeolite has a silica to alumina ratio in the range of from about 10 to about 30.

4. The process of claim 1 wherein the zeolite has a silica to alumina ratio in the range of from about 15 to about 20.

5. The process of claim 1 wherein said zeolite has a uniform particle size of about 1 to 1.5 mm.

6. The process of claim 1 wherein the zeolite is mordenite.

7. The process of claim 1 wherein the zeolite is in the acid form.

8. The method of claim 1 wherein said zeolite comprises less than about 1% by weight sodium oxide (Na)₂O) sodium.

9. The method of claim 1, wherein the gas is hydrogen chloride.

10. The method of claim 1, wherein the gas is hydrogen bromide.

11. The method of claim 1 wherein the zeolite comprises less than about 20ppm titanium.

12. The process of claim 1, wherein the zeolite is selected from the group consisting of ZSM-5(MFI), ZSM-11(MEL), β (BEA), faujasite usy (fau), hexagonal faujasite (EMT), Ferrierite (FER) and Chabazite (CHA).

13. The process of claim 1 wherein the zeolite is heated to about 700 ℃ prior to contacting with the gas.

14. A method for removing water from a gas comprising

(a) Heating a zeolite to about 400 ℃ for a first period of time sufficient to desorb physically adsorbed water from the zeolite, wherein the zeolite has a silica-to-alumina ratio of about 10 or greater;

(b) heating the zeolite to above about 650 ℃ for a second period of time, thereby forming a superheated zeolite;

(c) contacting the superheated zeolite with a gas; and

(d) the superheated zeolite is allowed to adsorb water from the gas.

15. The method of claim 14, wherein said heating to a temperature above about 650 ℃ is sufficient to dehydroxylate the zeolite for said second period of time.

16. The process of claim 14 wherein the zeolite has a silica to alumina ratio in the range of from about 10 to about 30.

17. The process of claim 14 wherein the zeolite has a silica to alumina ratio in the range of from about 15 to about 20.

18. The process of claim 14 wherein the zeolite has a uniform particle size of about 1 to 1.5 mm.

19. The process of claim 14 wherein the zeolite is mordenite.

20. The process of claim 14 wherein the zeolite is in the acid form.

21. The method of claim 14 wherein said zeolite comprises less than about 1% by weight sodium oxide (Na)₂O) sodium.

22. The method of claim 14, wherein the gas is hydrogen chloride.

23. The method of claim 14, wherein the gas is hydrogen bromide.

24. The method of claim 14 wherein the zeolite comprises less than about 20ppm titanium.

25. The process of claim 14, wherein the zeolite is selected from the group consisting of ZSM-5(MFI), ZSM-11(MEL), β (BEA), faujasite usy (fau), hexagonal faujasite (EMT), Ferrierite (FER), and Chabazite (CHA).

26. The method of claim 14 wherein the zeolite is heated to about 700 ℃ prior to contacting with the gas.

27. A method of preparing a dehydroxylated zeolite comprising:

(a) heating the zeolite at about 400 ℃ for a first period of time sufficient to desorb a first portion of physically adsorbed water therefrom; and

(b) heating the zeolite to above about 650 ℃ for a second period of time sufficient to remove a second portion of the water from the zeolite by dehydroxylation of the zeolite.

28. The process of claim 27 wherein the zeolite has a silica to alumina ratio in the range of from about 10 to about 30.

29. The method of claim 27 wherein the zeolite has a silica to alumina ratio in the range of from about 15 to about 20.

30. The process of claim 27 wherein the zeolite has a uniform particle size of about 1 to 1.5 mm.

31. The process of claim 27 wherein the zeolite is mordenite.

32. The method of claim 27, wherein the zeolite is in the acid form.

33. The process of claim 27 wherein said zeolite comprisesLess than about 1% by weight sodium oxide (Na)₂O) sodium.

34. The method of claim 27 wherein the zeolite comprises less than about 20ppm titanium.

35. The method of claim 27, wherein the zeolite is selected from the group consisting of ZSM-5(MFI), ZSM-11(MEL), β (BEA), faujasite usy (fau), hexagonal faujasite (EMT), Ferrierite (FER), and Chabazite (CHA).

36. A dehydroxylated zeolite having a silicon to aluminum ratio of about 10 or more and a low level of metal impurities, wherein the zeolite has been heated to a temperature of about 650 ℃ or more sufficient to cause dehydroxylation of the zeolite, and wherein the zeolite comprises less than about 20ppm titanium, less than about 100ppm iron and less than about 11ppm magnesium.

37. The zeolite of claim 36, wherein the zeolite has a silica to alumina ratio in the range of from about 10 to about 30.

38. The zeolite of claim 36, wherein the zeolite has a silica to alumina ratio in the range of from about 15 to about 20.

39. The zeolite of claim 36, wherein the zeolite has a uniform particle size of about 1 to 1.5 mm.

40. The zeolite of claim 36, wherein the zeolite is a mordenite zeolite.

41. The zeolite of claim 36, wherein the zeolite is in the acid form.

42. The zeolite of claim 36, wherein the zeolite comprises less than about 1% by weight oxygenDissolving sodium (Na)₂O) sodium.

43. The zeolite of claim 36, wherein the zeolite is selected from the group consisting of ZSM-5(MFI), ZSM-11(MEL), β (BEA), faujasite usy (fau), hexagonal faujasite (EMT), Ferrierite (FER), and Chabazite (CHA).

44. The zeolite of claim 36, wherein the zeolite is heated to a temperature of about 700 ℃.

45. A dehydroxylated zeolite having a silicon to aluminum ratio of about 10 or more and having a low level of metal impurities, wherein the zeolite has been heated to about 400 ℃ for a first period of time sufficient to desorb physically adsorbed water therefrom, and wherein the zeolite has been heated to a temperature of about 650 ℃ or more for a second period of time sufficient to cause dehydroxylation of the zeolite.

46. The zeolite of claim 45, wherein the zeolite has a silica to alumina ratio in the range of from about 10 to about 30.

47. The zeolite of claim 45, wherein the zeolite has a silica to alumina ratio in the range of from about 15 to about 20.

48. The zeolite of claim 45, wherein the zeolite has a uniform particle size of about 1 to 1.5 mm.

49. The zeolite of claim 45, wherein the zeolite is mordenite.

50. The zeolite of claim 45, wherein the zeolite is in the acid form.

51. The method of claim 45 wherein said zeolite comprises less than about 1% by weight sodium oxide (Na)₂O) sodium.

52. The zeolite of claim 45, wherein the zeolite comprises less than about 20ppm titanium, less than about 100ppm iron, and less than about 11ppm magnesium.

53. The zeolite of claim 45, wherein the zeolite is selected from the group consisting of ZSM-5(MFI), ZSM-11(MEL), β (BEA), faujasite USY (FAU), hexagonal faujasite (EMT), Ferrierite (FER), and Chabazite (CHA).

54. The zeolite of claim 45, wherein the zeolite is heated to a temperature of about 700 ℃ prior to contacting with the gas.